1. Field
The present invention generally relates to an objective of an angularly viewing, rigid endoscope, and particularly to an objective of the type referred to in claim 1.
2. Prior Art
Objectives of endoscopes have a number of problems, such as that endoscopes should usually be very thin which results in the fact that the objectives must have fewer millimeters in the diameter area. Rigid objectives also have the problem that they must be usually shaped angularly viewing, wherein the viewing direction of the objective is at an angle to the axis of the objective, in which the ray are emitted in a proximal direction through the main part of the objective, for example, directly onto an image receiver or an image guide conducting the image over the length of the endoscope. The change of direction of the beams between these two directions usually occurs by a prism arrangement.
DE 197 20 163 A1, FIG. 3 shows a generic objective, wherein the prism arrangement is comprised of two prisms, of which the proximal prism emits the rays after two reflections on mirrors in the direction of the axis of the objective. DE 35 37 155 C2 shows a similar design with an absorption layer.
So far unsolved problems occur on the second mirror. The second mirror must be limited in the direction of the passage area of the rays through the contact area, because it would otherwise partially interrupt the rays. However, if the second mirror does not protrude far enough in the direction of passage area, rays entering angularly with respect to the viewing direction can go past the second mirror and also the first mirror directly through the proximal prism into the proximal direction towards the viewer and generate disturbing effects there. For this reason, the second mirror must come as close as possible to the passage area. However, another effect will then interfere. Oblique rays which pass very inclined through the contact surfaces can be so inclined in the proximal prism between the mirrors that they again run back and forth, and are therefore reflected a total of four times. This also results in disturbances. The problem of the quadruple reflection is all the stronger, the smaller the slanted viewing angle is. The designer here is therefore at a dilemma between two interfering effects that occur at an either too long or too short mirror. An average length is also unsatisfactory because both effects can then occur.